The invention relates to a method for producing a connection between the neck area of a light metal cartridge, particularly an aluminium cartridge, and a plastic container inserted therein, by a drawing process that forms a connection area and applies areas of the wall of the light metal cartridge against the plastic container using a rotating main body of a drawing tool, said main body supporting at least one profiled drawing roller which can rotate about a rotation axis in order to delimit a tool working opening, the drawing roller lying against the outer surface of the light metal cartridge.
The invention further relates to a drawing tool which comprises a rotating main body having at least one profiled drawing roller arranged on a circular track and rotatable about a rotation axis, wherein the drawing roller delimits a tool working opening and can be moved out of a position that defines a minimum tool working opening, enlarging the diameter of the tool working opening, counter to the force of a spring, into a position that defines a maximum tool working opening.
For administering inhalable pharmaceutical active substance formulations, inhalers are used that can be held in the patient's hand and operated manually, in which the pharmaceutical active substance formulation is contained in an inhaler cartridge which, once the active substance formulation has been used up, can be removed from the inhaler and replaced by a new inhaler cartridge. The inhaler cartridge consists of an external aluminium cartridge and a plastic container inserted therein, often a plastic container produced by coextrusion, which comprises a rigid outer container and a flexible inner bag disposed therein. In order to create a pressure equalising opening between the inner bag and the outer container, an opening is formed in the relatively rigid outer container, for example by the so-called cut/crack-open process. The plastic container is filled with the pharmaceutical active substance formulation and sealed and inserted in the aluminium cartridge in the course of the manufacturing process to form the inhaler cartridge. In a subsequent step, a deformed wall portion is then formed in the aluminium cartridge in the upper part of the thus assembled inhaler cartridge, this deformed wall portion lying against the outer surface of the plastic container inserted in the aluminium cartridge. To form the connection area at the upper edge of the aluminium cartridge a drawing process is used in which a rotating drawing tool travels with its tool working opening from above over the connection area of the aluminium cartridge that is to be formed and thereby brings profiled drawing rollers arranged around the tool working opening into contact with the outer surface of the aluminium cartridge, so as to form the connection area by an axial movement. Then, in subsequent finishing steps, the aluminium cartridge is pressed in gastight manner against the outside of the plastic container arranged therein. Then the combination of the aluminium cartridge with the plastic container inserted therein is subjected to further processing and machining steps, at the end of which the finished inhaler cartridge filled with pharmaceutical active substance formulation is obtained.
Various drawing tools are known in the art for carrying out the drawing process. Thus, there are drawing tools in which the profiled drawing rollers are configured to be displacement-controlled to form the profiled connection area. However, because of the manufacturing tolerances occurring in the manufacture of aluminium cartridges and plastic containers, lastingly satisfactory results cannot be achieved with drawing tools of this kind. Therefore, drawing tools have also been developed in which the drawing rollers are guided and moved by force control. With drawing tools of this kind, however, only about 20000 inhaler cartridges can currently be produced in long-term operation.
In a force-controlled drawing tool known from the art, a tilting lever actuated by spring force is mounted externally parallel to the longitudinal axis of the drawing tool so as to be pivotable about a pivot axis arranged perpendicularly to the longitudinal axis of the drawing tool. On the side remote from the spring, the tilting lever bears on a slide that carries a drawing roller. As a result of the spring force acing on the tilting lever, when the aluminium cartridge is inserted in the tool working opening this and every other drawing roller of the drawing tool constructed in the same way is pressed against the outer surface of the aluminium cartridge. As a result, when the aluminium cartridge is inserted into the tool working opening, the drawing rollers are able to give way outwardly initially counter to the force of the spring acting on the tilting lever.
In the manufacturing process with this drawing tool the stationary aluminium cartridge and the rotational drawing tool are initially guided synchronously over one another at the same speed so that the aluminium cartridge is positioned underneath the tool working opening of the drawing tool. Then the drawing tool is lowered onto the aluminium cartridge from above while still rotating, as a result of which the drawing rollers surrounding the tool working opening come into contact with the outer surface of the aluminium cartridge and are thereby also set in rotation. The drawing tool is then lowered further until the drawing rollers have completely gripped the outer surface that is to be deformed in order to form the connection area. This lowering action causes the profiled drawing rollers to perform the drawing process and thereby deform the wall of the aluminium cartridge in the connection area such that the inside of the wall of the aluminium cartridge lies against the outer surface of the plastic container inserted therein. In order to achieve a uniform wall thickness of the aluminium cartridge and prevent damage to the plastic container or aluminium cartridge, the drawing rollers can give way radially outwards, as described hereinbefore, in displacement-controlled manner, counter to the force of the compression spring acting on the tilting lever. The minimum tool working opening selected in the drawing tool is thus adjusted to a lower limit of about 0.2 mm, so that when an aluminium cartridge that is to be processed is inserted the drawing rollers are always operating under prestress. With this force-controlled tool, totally satisfactory results have not yet been achieved in practice, because of the absence of equalisation of tolerances.
In displacement-controlled drawing tools, the problem is that they are not reliably capable of equalising the tolerances of the individual components of an inhaler cartridge, such as the plastic inner container, the plastic closure of the plastic inner container, the aluminium cartridge and a silicon seal that is to be fitted. Consequently, when the tolerances fall short, for example, so-called chatter marks are produced on the neck of the deformation region formed on the aluminium cartridge. When the tolerances are excessive, e.g. if the closure of the plastic inner container is too big or if an aluminium cartridge is formed with too small a diameter, the material that is deformed and displaced during the drawing process is pressed upwards and extends the neck of the aluminium cartridge in an undesirable manner. In the subsequent machining step of the inhaler cartridge, namely flanging, unattractive edges or even so-called burrs are produced.